1. Field of the Invention
The present invention relates to a wireless local loop system, and more particularly, to a wireless local loop system capable of interfacing with analog communication devices, such as a credit card referencing device, a smart pay-phone, a security system, a wireless inspection device, and the like.
2. Related Art
In general, a wireless local loop (WLL) system provides a wireless subscriber line that in a wireless manner connects a local switching center to a subscriber's premises (e.g., home or office), by way of radio waves, to provide voice, facsimile, and data communication services.
The WLL is also known as RITL (Radio In the Loop), FRA (Fixed Radio Access), FWA (Fixed Wireless Access), or FCS (Fixed Cellular System) in some countries. Many communication service providers have been recently drawn to the WLL system due to certain advantages that it provides over the currently used wired communication systems. The WLL system was designed by AT&T Bell Laboratory in the early 1970s for use in sparsely populated regions, such as fishing or rural villages, as an alternative to the current communication systems that require the installation of physical wire lines and cables. The intent was to save the cost associated with such installation throughout the sparsely populated areas by providing a wireless communication alternative.
Unfortunately, the WLL system was not a practical solution, at that time, due to difficulties associated with securing the right to use radio frequencies and also the high cost of manufacturing and installing antennas and radio transmitters and receivers. Semiconductor and electronic communication technologies, however, have developed rapidly since the 1990s. As a result of these developments, the efficiency and quality of wireless communication systems have improved. Today, manufacturers can produce more affordable wireless communication devices and equipment. At the same time, due to an increase in the number of subscribers and the reduction in the cost of production of radio equipment, total installation costs per subscriber is less expensive than ever. As such, the WLL system has started to draw the attention of many communication providers.
The WLL system can provide the following advantages over the current wired communication network systems. First, establishment of a wireless subscriber line and service is easier and faster than installation of a physical subscriber line that requires physically connecting a local switchboard to a subscriber's premises via a physical wire or cable. Second, the WLL system is a more durable and reliable system. For example, the WLL system can be used in case of emergency, if the current subscriber line networks are damaged due to a natural disaster, or the like. Third, the WLL system is technologically flexible to accommodate a variety of service requirements, such as POTS (Plain Old Telephone Service), data service, ISDN, and the like. Fourth, costs associated with installation of a WLL system is fixed, less dependent on distance and requires a relatively small initial investment. A quick and substantial return on the initial investment is, however, possible once the system starts to operate. Fifth, a WLL system network can be expanded quickly to accommodate an increase in subscriber communication bandwidth or subscriber base.
Because of the foregoing features, telephone and communication service providers, particularly those in developing countries that still utilizes POTS, consider the WLL system as one of the most effective methods for the quick construction of a subscriber communication network. Although the WLL system is similar to a mobile communication network in that both systems use radio channels as communication media, the advantage of WLL system is that it provides an electronic wave environment that is better than that of a mobile communication network because a WLL system does not require providing service to a mobile unit. Other advantages and features of the WLL system over a mobile communication network are discussed below.
A mobile communication network has a “non-line-of-sight” wave propagation environment. That is, the receiving and transmitting antennas in a mobile communication network are frequently located at a place lower than the surrounding buildings. As a result, generally, a straight carrier wave after transmission is blocked, reflected, and refracted in its straight path before it reaches a receiver in the mobile communication environment. Due to these obstructions, an average wave path loss in a range of 40 dB/decade can occur in a mobile communication network.
A WLL system environment, however, has a wave path loss as low as 20 dB/decade, because it provides a “line-of-sight” propagation environment, wherein the receiving and transmitting antennas are located at rooftop levels and unobstructed by buildings and other natural or manmade obstacles. Further, since the mobility of antennas in the WLL system is limited (i.e., all the stations are stationary), the same power can used to serve a larger area.
The electronic wave environment of the WLL system is implement over a point-to-point communication network structure, where each point is a stationary base stations. Said environment is less susceptible to distortion and weak signal strength in comparison to the electronic wave environment of a mobile communication network that includes a point-to-mobile network structure, wherein the electronic waves may have to propagate in multiple paths before they reach the intended destination.
In a mobile communication network, much overhead is associated with managing signals and tracking a mobile station in anticipation of a hand-off procedure. A hand-off procedure ensures the continuity of service throughout the mobile communication network by establishing a new line of communication between a mobile station and a new base station when the mobile station moves out of the territory of an old base station and into the territory of the new base station. Since the WLL system does not support mobile stations, the WLL system does not require reserving radio channels that are necessary to handle the overhead associated with the hand-off procedure. Thus, all radio channels may be used to route general calls, thereby improving communication bandwidth and efficiency.
Further, in the WLL system, a direct radio link between a building and a base station can be established for reducing interference to a particular subscriber. Because there is no change in the radio link unless the number of subscribers substantially increases or the area covered by the base station (i.e., a cell) is divided, the design of the WLL is substantially simpler than a mobile communication network.
Moreover, the stationary radio communication of the WLL system permits the use of directional antennas on forward/reverse links for reducing identical channel interference to respective subscribers, and in turn allows for shortening the distance in which the same frequency can be reused. The reduction of frequency reuse distance results in an increase in subscriber capacity per unit area.
Typically, the WLL system includes a telephone set, an NIU (a Network Interface Unit), a base station, a base station controller, and a base station managing device. The NIU makes wireless communication between the telephone set and a local switching center possible and is the end point in the WLL system that performs functions such as transmission/reception of a radio signal, modulation/demodulation of a radio channel, voice compression/restoration, and providing access to a PSTN terminal.
Depending on the applied technology, various forms of terminals with built-in or separate RF functions may be available. The terminals may also be in the form of a handset or its equivalents and may support single or multiple communication lines.
The base station is located between the NIU and the base station controller in the communication path. The base station connects to the NIU by radio and to the base station controller by wire. The base station performs the following functions: transmission/reception of radio signals, power control, modulation/demodulation of channels, and protocol transform for signal transmission/reception between the NIU and the base station controller. The base station includes an antenna transmitter/receiver, a power amplifier, channel cards and hardware for interface with the base station controller.
Radio access between the NIUs and the base stations is limited by an effective cell radius that is determined based on limitations in the electronic wave environment and the transmission power. The base station controller provides for effective communication between the wireless and wired portions of the WLL system. The base station controller is located between the local switching center and the base station, for connecting the local switching center and the base station. It is also responsible for managing the base station. The base station controller is generally connected to respective base stations by wire and manages the base stations, radio resources, transcoding, and the function that determines a base station's respective switchboard match.
The base station managing device is responsible for managing and maintaining the entire equipment of the WLL system and other functions including network system management, performance management, data processing, software management, security management, and the like.
A WLL system includes a telephone set and a NIU. There are two types of WLL systems: separate and integrated. A separate WLL system has a stationary telephone set and a separate NIU that can be connected to the stationary telephone by way of a wire. The separate NIU can be purchased when a subscriber having a stationary telephone set connected to an existing wire network intends to subscribe to a WLL service. An integrated WLL system includes a telephone set and a NIU integrated into a self-contained one-piece hardware unit, intended for use by a subscriber who has no stationary telephone set connected to an existing wire network.
FIG. 1 illustrates a block diagram of a WLL system. As shown, the WLL system is provided with a RF transmission/reception mechanism 11. The RF transmission/reception mechanism 11 receives a RF signal provided by an antenna. The antenna has a transmission frequency range of 824–849 MHz and a reception frequency range of 869–894 MHz provided by a super heterodyne system. After receiving an RF signal from the antenna, the RF transmission/reception mechanism 11 produces an IF (Intermediate Frequency) signal and converts the IF signal into a digital baseband signal through an amplifier and an analog/digital converter. The digital baseband signal is then provided to an MSM 12 (Mobile System Modem).
The RF transmission/reception mechanism 11 also operates to receive a digital baseband signal provided by the MSM 12 and to convert the digital baseband signal into an analog signal producing an intermediate frequency signal. The RF transmission/reception mechanism 11 converts the IF signal into a RF band signal for transmission. The RF band signal is provided to the base station through the antenna.
The MSM 12 decodes a digital baseband signal provided by the RF transmission/reception mechanism 11 to produce information data. The information data is then coded and converted into a digital baseband signal and is thereafter provided to the RF transmission/reception mechanism 11. A CODEC 13 codes an analog voice signal provided by a microphone in the handset into a digital voice signal. The digital voice signal is then provided to the MSM 12. The digital voice signal is decoded by the MSM 12 into an analog voice signal.
Levels of respective voice signals are adjusted and provided to a speaker in a handset 14. The handset 14 is connected to the CODEC 13 by a coil line having a speaker for presenting the analog voice signal provided by the CODEC 13 and a microphone for providing an analog voice signal to the CODEC 13 and a RS-232C driver 15 for line connection between an external device (e.g., a computer) and the WLL system for carrying out serial communication.
The modes of operation of the WLL system of FIG. 1 are provided below. First, the reception mode is explained and thereafter the transmission mode. A hook detecting mechanism (not shown) detects the on/off status of the hook switch and provides the status information of the hook switch to the MSM 12. The MSM 12 always determines the on/off status of the hook switch. Accordingly, when an antenna signal is received from the base station in a state when the hook switch is off (i.e., the handset is on the hook), a ring signal is provided to a user. The RF transmission/reception mechanism 11 receives the RF signal from the antenna, produces an intermediate frequency IF signal, converts the IF signal into digital baseband signal, and provides the digital baseband signal to the MSM 12.
The MSM 12 decodes the digital baseband signal provided by the RF transmission/reception mechanism 11 to produce information data. The MSM 12 then provides the information data to the CODEC 13. The CODEC 13 decodes the digital voice signal provided by the MSM 12 into an analog voice signal, adjusts levels of respective voice signals, and presents a voice signal through the speaker in the handset 14.
In transmission mode, an analog voice signal received through the microphone in the handset is coded at the CODEC 13 into a digital voice signal that is provided to the MSM 12. The MSM 12 receives the digital voice signal, converts the coded digital voice signal into a digital baseband signal, and provides the digital baseband signal to the RF transmission/reception mechanism 11. The RF transmission/reception mechanism 11 receives the digital baseband signal provided by the MSM, converts the digital baseband signal into an analog IF signal, and converts the IF signal into a RF baseband signal intended to for transmission. The RF band signal is then provided to the base station through the antenna. In this manner, the WLL system completes transmission to the base station.
When a user tries to make a phone call, the user picks up the handset 14. Picking up the handset 14 turns on the hook switch. The user then dials a telephone number on a key pad (not shown) causing a radio channel for communication to be assigned to the WLL system in the manner explained above. The WLL system may be connected to a personal computer through the RS-232C driver 15 for digital data transmission/reception.
Unfortunately, the WLL system discussed above is incapable of interfacing with analog communication devices, such as a credit card referencing device, a smart pay-phone, a security system, a wireless inspection device, or a computer with a built in MODEM. Thus, an improved WLL system is needed that allows regular data transmission/reception to/from said analog communication devices.